In a mobile communication system such as IMT-2000, transmission power control is performed from the viewpoint of enlargement of circuit capacity and economy of battery of a mobile station and the like. For example, quality measurement of a channel is performed in a receiving side, and a transmission power control (TPC) bit is transmitted by a return channel (DPCCH, for example) such that the channel that is being received satisfies desired quality. As a result, the transmission power is updated by 1 dB, for example, and quality measurement and transmitting/receiving of the TPC bit are repeated, so that the transmission power can be gradually changed to be closer to an optimal value. That is, in a communication of a circuit switching scheme, an individual channel is assigned specifically to a mobile station, and the transmission power of the mobile station is gradually adjusted based on a temporally continuing history on the transmission power. Such transmission power control is described in a non-patent document 1, for example.
[Non Patent document 1] Keiji Tachikawa, “W-CDMA mobile communication scheme”, MARUZEN, pp. 126-128